A primary aim in the art is to increase the proportion of input energy that appears in the laser output. This problem is essentially one of achieving improved impedance matching, and prior workers have adopted the use of low impedance switches, called "rail gaps" or "sharpening gaps," to aid in achieving a better impedance match between the energy storage network and the electrical discharge. The result has been increased laser efficiency and an increased laser pulse length. Such a sharpening gap has been located external to the laser envelope and has exhibited a low impedance by virtue of employing a series of arcs distributed in parallel along the length of the device. Such a sharpening gap can be triggered by a further electrode or some other suitable external means.
However, such sharpening gaps have proved to be cumbersome devices with relatively short reliable lifetimes before electrode pitting becomes severe.